1. Field of the Invention
The present invention relates to an apparatus for speech signal processing and a method for speech signal processing intended to improve the intelligibility of speech signals in a hearing aid or a public address system.
2. Description of the Prior Art
Hitherto there has been much study directed to the speech signal processing apparatus for the purpose of improving intelligibility for the hard of hearing, of such an example being disclosed by R. W. GUELKE in "Consonant burst enhancement: A possible means to improve intelligibility for the hard of hearing," Journal of Rehabilitation Research and Development, Vol. 24, No. 4, Fall 1987, pp. 217-220.
In such a conventional apparatus for speech signal processing, the input speech signal is first fed into a gap detector, an envelope follower, and a zero crossing detector. Next, the burst of the stop consonant is detected by the gap detector, envelope follower, differentiator, and zero crossing detector. In response consequence, a the one-shot multivibrator delivers pulses for a specific interval corresponding to the burst of the stop consonant to an amplifier. Finally, the amplifier amplifies the input speech signal by a specific amplification factor for the duration of the interval of the pulses delivered by the one-stop multivibrator.
In such a prior art arrangement, it is difficult to detect the burst of the stop consonant, and it is particularly difficult when noises are superposed. Further, only the stop consonant can be enhanced, and many other consonants cannot be enhanced. Still further, since the interval to be amplified and the amplification factor are constant, it is impossible to follow up changes.